The committee of scientists who met at the WHO International Agency for Research on Cancer in Lyon, France, earlier this year, recanted a previous statement that coffee and mate themselves might increase the risk of developing cancer, expressing concern over the temperature rather than the contents of the beverage.

"Enjoy your coffee or mate, but make sure it's not very hot," said Mariana Stern, PhD, an associate professor of preventive medicine and urology at the Keck School of Medicine of the University of Southern California.

"There is physical evidence that very hot beverages can contribute to cell injury in the esophagus and thus contribute to cancer formation."

Researchers assessed data from more than 1000 studies on 20 different types of cancer, determining that drinking scalding beverages is probably carcinogenic. This classification places temperature of the beverage at the same level of carcinogenicity as DDT and human papillomavirus.

"We were now able to evaluate more carefully the effect of mate itself from the effect of temperature, and we concluded that the observed links between mate drinking and cancer of the esophagus seem to be largely driven by drinking mate very hot," Stern explained.

"Similar associations are seen for other very hot beverages, like tea or coffee."

The researchers downgraded coffee from possibly carcinogenic and mate from probably carcinogenic to safe so long as the beverages are not scalding. WHO classified coffee as possibly carcinogenic in 1991, based on a smaller database that was likely affected by tobacco smokers within the database. Tobacco smoking is highly correlated with high consumption of coffee.

This analysis also determined that drinking a cup of coffee each day decreases the risk of developing liver cancer by approximately 15%. Regular coffee consumption also decreased the risk of developing uterine endometrium cancer.

"For many cancer types, we found clear evidence that coffee is not carcinogenic," Stern said.

"In fact, we found that coffee protects against some cancers such as liver and uterine endometrium cancer."

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